The formation of mixtures of epoxy resin esters and maleinized oils or other maleinized organic derivatives is known. French Patent No. 69 25 181, describes coating products which are water soluble after neutralization, comprising reaction products of diene polymerizates with alpha, beta-unsaturated carboxylic acids or anhydrides and at least one thermoreactive condensation product of formaldehyde and phenol-carboxylic acids, and other optional constituents. Among said optional constituents, ethylene glycol, propylene glycol and other saturated diols are mentioned, as well as are mentioned derivatives of diphenylol propane and epichlorohydrin, said derivatives being esterified by fatty acids, whereby they contain no free oxirane groups. In U.S. Pat. No. 3,518,212, a process is described according to which monoepoxide esters are prepared and the latter are then reacted with a polycarboxylic acid resin comprising the reaction product of an alpha, beta-unsaturated carboxylic diacid or an anhydride of said diacid, coupled with a siccative oil and other diene derivatives.
According to the process described in U.S. Pat. No. 3,518,212, the reaction of the polycarboxylic acid resin with the monoepoxide ester should be effected at a temperature of about 85.degree. C. for a period of time of from 30 minutes to 1 hour, it being specified that temperatures above 120.degree. C. are to be avoided since higher temperatures give rise either to an excessive formation of foam when the reacting products comprise water, or to a side esterification of the --OH groups when the reacting products do not comprise water. Furthermore, it is specified that the ester is produced in the presence of a tertiary amine.